The current therapy with implantable cardioverter/defibrillators (ICD) is lacking specificity. The technical concept of arrhythmia detection, as a single channel ventricular rate threshold does not provide a clear differentiation between supraventricular and ventricular rhythms. Nearly 25% of all ICD-therapies are related to a false positive detection of supraventricular arrhythmias.The use of alternative, non rate based detection algorithms is limited due to the reduced long-term stability of the sensors and due to a high battery drain. Based on the current concept of arrhythmia detection, the use of additional timing algorithms as the variability of consecutive RR-cycle length ("Rate-Stability") and the detection of a sudden acceleration in the ventricular rate ("Rate-Onset") provide a clinical relevant increase in specificity in ICD-therapy. A further class of detection algorithms uses the morphologic assessment of intracardiac electrograms. Despite the fact that these morphology based algorithms have shown a high sensitivity and specificity in the discrimination between ventricular and non-ventricular rhythms, only one algorithm was implemented in ICD-generators and the clinical importance in ICD-therapy was very small. In 1995 a new morphology based detection algorithm was introduced in ICD-therapy. The "width criterion" is based on the measurment of the duration of the intracardiac signal. In 1995 and 1996 the first two series of a dual chamber ICD system were introduced in clinical ICD-therapy. These devices provide a two-channel atrio-ventricular arrhythmia detection in connection with a DDD antibradycardia pacing therapy. The use of DDD-ICD systems is expected to be a great step forward to enhance diagnostic specificty. A number of rate and timing detection algorithms and algorithms comparing the assoziation of atrial and ventricular signals may improve the discrimination between supraventricular and ventricular tachyarrhythmias. The future implementation of additional morphology based detection algorithms in DDD-ICD systems may solve the problem of the limited detection specificity in clinical ICD-therapy.